main/linux-postmarketos-qcom-msm8974: upgrade to 5.9.0_rc4

Based on !1536 (merged)

Tested devices:

• fairphone-fp2 (me)
• lg-hammerhead @unrznbl
• oneplus-bacon @symmetrist
• samsung-klte @minlexx @ichernev
• sony-amami ?
• sony-castor @plata-gl @julianuu
• sony-sirius ?

@konradybcio Would be good to add sony-honami patches to the repo as well?